The present invention relates to an X-ray image capturing apparatus, an X-ray imaging system and an X-ray image creation method.
Conventionally, almost of all X-ray images to be used for diagnosis purpose have been acquired by employing the absorption-contrast X-ray method. According to the absorption-contrast X-ray method, contrasts in an X-ray image are formed corresponding to differences between X-ray intensities generated after X-rays have penetrated through the subject. On the other hand, instead of employing the X-ray absorbing action, the phase-contrast method has been proposed as another method for acquiring the contrasts in the X-ray image, which employs the X-ray phase change action. For instance, there has been put in practice such a phase-contrast image capturing operation that acquires an X-ray image having a high visibility by employing the edge enhancement processing, which utilize the X-ray refraction at the time of an enlarged image capturing operation, as set forth in, for instance, Tokkai 2007-268033 and Tokkai 2008-18060 (both are Japanese Patent Application Laid-Open Publications).
The absorption-contrast X-ray method is effective for capturing an X-ray image of such a subject that has a relatively large X-ray absorption rate, such as a born, etc. In contrast, according to the phase-contrast X-ray method, it is possible to visualize even such soft tissue portions, such as a breast tissue, a cartilage of a joint, a soft tissue around a joint, images of which are hardly acquired by employing the absorption-contrast X-ray method, due to the small X-ray absorption rate. Accordingly, it is expected to widely introduce the phase-contrast X-ray method into the X-ray image diagnosing field.
As one of the radiographic image capturing apparatus employing the phase-contrast method, it has been considered to put the Talbot interferometer that employs the Talbot effect into practice, as set forth in, for instance, Tokkaisho 58-16216, Tokkai 2007-203063 (both are Japanese Patent Application Laid-Open Publications) and WO 2004/058070 Pamphlet (International Publication). The Talbot effect is defined as such a phenomenon that, when coherent light penetrate through the first grating in which plural slits are formed at constant intervals, a grating image thereof is focused at a constant period in the light traveling direction. This grating image is called a self-image. In the Talbot interferometer, the second grating is disposed at the focal position of the self-image, so as to measure interference fringes (Moire fringes) generated by slightly shifting the second grating. Since a pattern of the Moire fringes is deformed by placing an object in front of the second grating, when the Talbot interferometer is employed for the X-ray image capturing operation, it is possible to acquire a reproduced image of the subject by irradiating coherent X-rays onto the subject placed in front of the first grating and by applying an arithmetic calculation processing to the acquired Moire image.
Considering the practical realization, it has been expected to put the Talbot-Lau interferometer, in which a multi slit element is disposed between an X-ray source and the first grating so as to increase the amount of X-rays to be irradiated onto the subject, into practice.
For instance, when the Talbot-Lau interferometer is employed for capturing an X-ray image to be used for diagnosing the rheumatic disease, it is preferable that the X-ray image capturing apparatus is configured as a vertical type, in which the X-rays are irradiated onto the subject in a direction of gravitational force from the ceiling to the floor. If vertical type, it becomes easy to capture an image of the hand or the like at which the rheumatic is liable to be developed, and it becomes possible to reduce the installation area on which the X-ray image capturing apparatus is to be installed.
According to the conventional Talbot-Lau interferometer, when a reconfigured image is created by employing the stripe scanning method, a plurality of Moire images, which are different from each other in phase of strips corresponding to the relative positions of the first grating and the second grating (hereinafter, referred to as the Moire images at constant periods), is captured by shifting the first grating and the second grating (relatively shifting both the gratings). In the case that the X-ray image capturing apparatus is configured as a vertical type in order to reduce the installation area on which the concerned apparatus is to be installed, the first grating and/or the second grating are/is disposed at such a position that is nearer to the floor than that of a driving system for moving them, namely, disposed in the vicinity of the feet of the patient. In this structure, there would arise such a fear that the patient would contact the housing of the driving system, and as a result, unexpected impacts or vibrations are incurred to the gratings. Further, when the patient rides on the wheelchair, the space around the feet of the patient becomes narrower than ever, the abovementioned vibration problem has been liable to occur. Since it would be concerned that the high precision shift control cannot be achieved under such the vibration occurring environment, it is necessary for the operator to wait the X-ray image capturing operation until the influence of the vibration is eliminated. Further, it should be necessary to guide the patient to an appropriate position so as not to contact the housing of the driving system located in the vicinity of the patient's feet, and as a result, the direction of inserting the patient's hands or the like into the subject placing plate is limited. Alternatively, it should be necessary to request the patient of relatively advanced age to stretch the patient's hands or the like from the position being apart from the subject placing plate. As a result, since a certain stress is imposed to the patient concerned, such the practice is not preferable.
Since such the inconveniences as abovementioned have been predicted so far, it has been considered that it is difficult to put the X-ray image capturing apparatus, which employs the Talbot-Lau interferometer configured as the vertical type, into practice.